I ran a cheap top cap mount from ebay for ages, but recently upgraded it to a k-edge. Only because the cheap one never had a very firm lock on my Wahoo and it would wiggle squinty during a ride. I bought a new K-Edge insert to pop into it but found that it was too big for my top cap, so I just went ahead and bought a K-Edge top cap. It’s an expense that’ll be forgotten in no time I guess,
You may find you need to run a 5mm (I prefer 10mm) spacer on top of your step if you have a short stem, in order for your computer to clear the faceplate (I needed to on a 40mm Renthal Apex stem).